The development of the 3 millisecond response time thermistor has been completed and incorporated into a stopped-flow apparatus. It will be used in the study of the reaction of carbon dioxide and phosphates with hemoglobin at various stages of oxygenation. Lycra coatings for pH electrodes have proved very effective in protecting electrodes from the effects of protein. This new electrode will be introduced into both stop flow titration and PCO2 electrode systems. Difficult problems associated with the manufacture of observation tubes for the high speed optical flow apparatus have been overcome and clean signals with a consistent time resolution of 200 microseconds are presently being obtained. The kinetics of reaction of calcium and EGTA at 25 degrees C and 4 degrees C over the pH range of 6.5-7.5 will be continued on this instrument. The laser flash photolysis apparatus for studying the very fast reactions of oxygen in both hemoglobin solutions and red cell solutions has been initiated and the laser has been set up and operated. The optical system and cell hemoglobin studies have been constructed and installed. A system for observing these reactions directly in the red cells is presently under construction. It is based on the "Optisat" principle of using two near-infrared wavelengths to observe the O2 plus Hb yields O2Hb reaction.